1. Field
The field of the invention is endless track drive systems for snow transversing vehicles, more particularly drive sockets wheels for such vehicles.
2. State of the Art
In contrast to traditional caterpillar vehicles, military tanks, and the like, vehicles for use upon snow are necessarily as light as possible and employ propulsion tracks having much greater ground-contacting areas. Substantially, the entire area beneath the vehicle body is occupied by the drive tracks, which typically extend both longitudinally and laterally beyond the vehicle to provide further bearing area. This large bearing area is needed both to secure traction upon the soft, easily sheared snow and to avoid undue sinking. The extremely wide tracks must nevertheless be as light as possible. Conflicting needs for large area and low weight has led to the use of tracks comprising thin, flexible, reinforced rubberoid belts with affixed transverse snow-engaging cleats called grousers. Such tracks are much lighter than the massive, transversely hinged metal tracks found on the above mentioned traditional vehicles. However, because of their great flexibility, further aggravated by plasticity and elasticity, these tracks are more difficult to retain upon the vehicle. Typically, the body of the vehicle is carried upon tire equipped bogie wheels which bear upon the bottom, ground contacting, driving portion of the belt. The upper, coasting portion rests upon the top of the bogie tires. Lateral forces from vehicle turning or operation upon laterally inclined snow surfaces tend to cause side slip of the belt across the bogies. This is countered by inwardly projecting upstanding pairs of tire guides provided upon each grouser, spaced laterally to accommodate the tires in between. Rearwardly of the bogies is a drive sprocket wheel, the teeth of which engage the grousers to propel the vehicle. Loss of the belted track off the vehicle at the bogies is a matter of real concern. The plastic creep of the belt precludes any great reliance upon high tension to hold it upon the bogies. Necessarily rather loosely strung, the belt may permit the restraining tire guides to be climbed by the bogie tires, even releasing the track assembly entirely from the vehicle. Heretofore, the drive sprocket wheel has been constructed of thin metal with rims of limited width, providing necessary strength and minimizing weight. For reduced wear of both the grousers and the sprocket wheel teeth, the grouser contacting portions of the teeth are typically coverd by a thin layer of hard plastic, which also greatly reduces the operating noise from the drive system. Such sprocket wheels adequately drive the track, but do little if anything to alleviate the belt stability problem, and their potentially helpful role if appropriately designed has not been recognized.
Clearly, a pressing need exists for a sprocket wheel designed to assure or at least contribute to the stability of the wide, lightweight highly flexible belt assemblies used on snow traversing vehicles.